1. Field of the Invention
This invention relates to winding devices for cameras, and more particularly to a winding device for a camera such that when the exposure is terminated, winding of the photographic film and charging of the shutter and mechanisms associated therewith are performed by the action of one series of driving power so that the next exposure is ready to be performed.
2. Description of the Prior Art
In general, the winding device in a camera must change the angle of rotation of the spool for one-frame advancement of the film as the number of film frames exposed increases. This is because the diameter of the film wound on the spool is increased with decrease in the angle of rotation of the spool to advance the film through the length of one frame. Incidentally, the shutter and other mechanisms associated therewith are charged by an actuator which is required to always operate in a constant fashion regardless of the change of the frame number. Therefore, the conventional winding devices are generally constructed so that driving power of the driving means is transmitted directly only to the takeup spool to wind up the film thereon, and this moving film is used to drive a sprocket to rotate to a certain degree (necessary to move the film by one frame) by which the shutter is charged. In such winding device, however, as has been described above, the direct transmission of power from the driving source to the takeup spool is combined with the indirect transmission of the driving power to the charging mechanism for the shutter through the film, thereby making unavoidable increase in the complexity of the winding device. Another disadvantage is that so long as film is not loaded, the camera cannot be operated.
In recent years, therefore, it has also been proposed to provide the winding device with a clutch mechanism operating in such a manner that while a certain amount of power from the driving means is transmitted directly to both of the takeup spool and the charging member for the shutter or the like, the transmission of the driving power to the takeup spool is cut off when the film is advanced one frame, thus changing the angle of rotation of the takeup spool depending upon the diameter of the film wound thereon. With such device, the above-mentioned problem that the lack of film leaves the camera in the idle state can also be eliminated. However, even such winding devices of the conventional type have alternative disadvantages, since the clutch mechanism for use in transmitting motion to the film is arranged to be closed or engaged (effective for transmission of the driving power) in response to either an actuation of camera release, or the termination of running down movement of the shutter. That is, in a case where the closing operation of the clutch mechanism is controlled by the release actuation, the actuator for releasing the camera must be designed to move through a longer stroke, or with a stronger force of depression, giving the user an unpleasant impression and increasing the possibility of producing drawbacks such as camera vibration. In the other case where the above-described closing operation of the clutch mechanism is coordinated with the closing operation of the shutter, as the shutter shares the available energy which must be large enough to change over the clutch mechanism, the shutter is apt to bind at the terminal end of the running down movement. Particularly, in an application of this winding device to lens shutter-equipped cameras, there is another disadvantage that because of the small kinetic energy of the shutter blades, the reliability of controlling the changing operation of the clutch mechanism is considerably lowered.
The use of an electric motor as the driving means in such winding device also gives rise to an additional problem. That is, as the output of the motor is drivingly connected to the film transportation mechanism and the shutter charging mechanism, and the current supply to the motor is cut off when each cycle of charging operation is completed, it often happens that the feeding of the film from the cartridge terminates before the last film frame is fully advanced. If so, because of the fixture of the terminal end of the film strip to the supply spool in the cartridge, a further winding of the film is no longer possible, and the motor is braked hard while current flow thereto continues. This causes flow of a far larger current to the motor than when it rotates. Since the batteries used in the cameras are generally of small capacity, the allowance of such large current to flow results in a premature consumption of electrical energy in the battery. Further, when such a situation is permitted to exist for a long time, the motor and battery generate heat, causing accidental damage.
In order to avoid such drawbacks, according to the prior art, upon making sure that the end of feeding of the film has occurred, the operator must manipulate a switch so that the current supply to the motor is cut off. With such construction and arrangement, however, the burden on the operator is increased, the management of the camera is complicated, and, when the necessary operation of the switch is overlooked, the above-described drawback is encountered. To avoid such difficulties in the operation of the camera, there has also been proposed a method of automatically cutting off the current supply to the motor by using, for example, an electrical delay circuit. This circuit is actuated when each cycle of film winding operation starts, and then produces a de-actuating signal for the current supply control switch only when that cycle is not completed within the prescribed time. The employment of this method, however, gives rise to problems in that provision must be made for an electrical control means in the form of the above-described delay circuit, and that the normal operation of the above-described delay circuit must be protected against a loss in the voltage of the battery by using an additional complicated circuit. It is, therefore, not compatible with a battery of small capacity such as is adapted to be accommodated in the camera housing.